Serialport read write in java

I have an application where i need to write some data to the serial port and get the response from it. Now the sequence is as follows:

1. Send a message to the serial port.
2. wait for the response
3. Once the response is received i have to process the message and until then nothing should happen to the application.

How should i break this problem and solve it ? I am not good in serial programming. I have tried a code but my application halts when i execute the send message. May be because i am reading the message just after sending a message. I really don't know hot to break this problem down. Do i have to start listen to the port during the application start ? Do i have to keep the port open ? Is it ok if i open the port every time i need that ? and how should i make the program wait to respond until the response message is read form the port ? Please help me solve this problem..

--EDIT--

package testConn;  
import forms_helper.global_variables;  
import java.io.IOException;  
import java.io.InputStream;  
import java.io.OutputStream;  
import java.util.logging.Level;  
import java.util.logging.Logger;  
import javax.comm.*;  
import java.util.*; 

/** Check each port to see if it is open. **/  
public class openPort implements SerialPortEventListener {

    static Enumeration portList;
    static CommPortIdentifier portId;
    static String messageString;
    public static SerialPort serialPort;
    static OutputStream outputStream;
    InputStream inputStream;
    static boolean outputBufferEmptyFlag = false;

    public void open() {
        Enumeration port_list = CommPortIdentifier.getPortIdentifiers();

        while (port_list.hasMoreElements()) {
            // Get the list of ports
            CommPortIdentifier port_id = (CommPortIdentifier) port_list.nextElement();
            if (port_id.getName().equals("/dev/ttyS1")) {

                // Attempt to open it
                try {
                    SerialPort port = (SerialPort) port_id.open("PortListOpen", 20);
                    System.out.println("Opened successfully");
                    try {
                        int baudRate = 9600; //
                        port.setSerialPortParams(
                                baudRate,
                                SerialPort.DATABITS_7,
                                SerialPort.STOPBITS_1,
                                SerialPort.PARITY_EVEN);
                        port.setDTR(true);
                       /*

                        port.setFlowControlMode(
                                SerialPort.FLOWCONTROL_NONE);
                        *
                        */
                        System.out.println("properties are set");
                    } catch (UnsupportedCommOperationException e) {
                        System.out.println(e);
                    }
                    try {
                        //input = new SerialReader(in);
                        port.addEventListener(this);
                        System.out.println("listeners attached" + this);
                    } catch (TooManyListenersException e) {
                        System.out.println("too many listeners");
                    }
                    port.notifyOnDataAvailable(true);
                    //port.notifyOnOutputEmpty(true);
                    //sendMessage(port,"@PL");
                    //port.close ();
                    try {
                        inputStream = port.getInputStream();
                        System.out.println("inputstream" + inputStream.available());
                        outputStream = (OutputStream) port.getOutputStream();

                    } catch (IOException e) {
                        System.out.println(e);
                    }

                    //set the created variables to global variables
                    global_variables.port = port;
                    global_variables.inputStream = inputStream;
                    global_variables.outputStream = outputStream;
                } catch (PortInUseException pe) {
                    System.out.println("Open failed");
                    String owner_name = port_id.getCurrentOwner();
                    if (owner_name == null) {
                        System.out.println("Port Owned by unidentified app");
                    } else // The owner name not returned correctly unless it is
                    // a Java program.
                    {
                        System.out.println("  " + owner_name);
                    }
                }
            }
        }
    } 

    public static void sendMessage(SerialPort port, String msg) {
        if (port != null) {
            try {                
                global_variables.outputStream.write(msg.getBytes());
                global_variables.outputStream.flush();
                try {
                    Thread.sleep(2000);  // Be sure data is xferred before closing
                    System.out.println("read called");
                    //SimpleRead read = new SimpleRead();
                    //int read = global_variables.inputStream.read();
                    //System.out.println("read call ended"+read);
                } catch (Exception e) {
                }
            } catch (IOException ex) {
                Logger.getLogger(openPort.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }

    public void serialEvent(SerialPortEvent event) {
        System.out.println(event.getEventType());
        switch (event.getEventType()) {
            /*
            case SerialPortEvent.BI:

            case SerialPortEvent.OE:

            case SerialPortEvent.FE:

            case SerialPortEvent.PE:

            case SerialPortEvent.CD:

            case SerialPortEvent.CTS:

            case SerialPortEvent.DSR:

            case SerialPortEvent.RI:


            case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
            System.out.println("event.getEventType()");
            break;
             *
             */

            case SerialPortEvent.DATA_AVAILABLE:
                System.out.println("inside event handler data available");
                byte[] readBuffer = new byte[20];
                try {
                    while (inputStream.available() > 0) {
                        int numBytes = inputStream.read(readBuffer);
                    }
                    System.out.print(new String(readBuffer));
                    System.exit(1);
                } catch (IOException e) {
         开发者_如何学Go           System.out.println(e);
                }

                break;
        }
    }
}

What is wrong with this code ? I cant see the response from the terminal connected to serialport when i send a polling message. I am opening the connection at my application start and i am sending the message when a button inside my application is clicked. How do i solve the problem ??

See this wikibook, section Event Driven Serial Communication.

Previously answered question, here: How do I get Java to use the serial port in Linux?

Depending on your platform (if you are on a *NIX box) you can often get away with using stty to set the baud rate/port settings, and then simply open the /dev/tty* port with a FileInputStream/FileOutputStream. I used to have a chunk of code that did that and worked quite reliably, but now that I go looking for it it appears to have been misplaced. Sad.

Try to retryger the tx again after than the once and when keep the Rx on read for debugg the came back message from the device